The present invention provides a determination method to obtain the optimum image output quality. The method comprising the standard white plate is scanned prior to the scanning document sheet to obtain a first image data. Then, the first image data is calculated to generate the shading curve, noise level, and brightness data, which corresponding to each sensor device. Next, the shading curve or standard values returned to input into the calibration database. Thereafter, the scanning device scanned and exposed the document sheet to obtain a second imaging data that corresponding to each sensor device and to read out the standard curve (shading curve) from the calibration memory simultaneously. Next, a determination method utilized to determine the difference value between the two pixels at neighboring position, if the difference value is smaller than the standard value, then the two neighboring pixels is to be averaged and outputted the average value; else, the output pixel value is equal to the original position of the pixel value. Finally, the corrected image data is outputted which is corrected by calibration method.